The synthesis of well-defined block copolymers continues to represent a difficult challenge in the field of polymer chemistry. The preparation of block copolymers by free radical, anionic, cationic and condensation techniques is surveyed in a review entitled "Recent Advances in Polymer Blends, Grafts and Block" L. H. Sperling, ed., pages 3-62, Plenum Press, New York, 1974; however, the characterization of these materials in terms of molecular weight, molecular weight distribution, solubilities, physical properties, etc., remains to be completed.
Anionic polymerization has been utilized to produce well-characterized block copolymers as described by M. Szwarc in Nature, 178, 1168 (1956) and by L. J. Fetters in "Block and Graft Copolymers" R. J. Ceresa, ed., pages 99-132, John Wilet-Interscience, New York, 1973.
In the field of cationic polymerizations, in contrast to the preceding frequently used techniques, well-defined block copolymers have been synthesized only in very few instances by oxonium ion polymerization of certain cyclic ethers. Thus Saegusa et al. as disclosed in Macromol., 3, 377 (1970) prepared a poly(tetrahydrofuran-b-bischloromethyloxetane) by first producing a "living" polytetrahydrofuran using BF.sub.3 -epichlorohydrin initiator in heptane at 0.degree. C., removing the unreacted tetrahydrofuran, and introducing to this system bischloromethyloxetane. Living polytetrahydrofuran oxonium ions have been coupled with living polystyryl anions by Berger et al. as disclosed in J. Polymer Sci., B, 4, 183 (1966). A similar technique was utilized by Yamashita et al. Macromol., 4, 548 (1971).
An abstract has been published at the International Symposium on Cationic Polymerization by Y. Jolivet and J. Peyrot, Communication C18, International Symposium on Cationic Polymerization, Rouen, France, Sep. 16-20, 1973. This abstract briefly describes a method for the synthesis of a poly(styrene-b-isobutylene); in this publication, both the resulting product and process utilized are different from that herein described and claimed; the Jolivet et al. process is one wherein a benzyl chloride initiator in conjunction with diethylaluminum chloride coinitiator polymerized isobutylene giving rise to a polyisobutylene containing a terminal benzyl group ##SPC1##
Followed by chloromethylation to ##SPC2##
Followed by introduction of styrene and Et.sub.2 AlCl to give ##SPC3##
where PSt = polystyrene and PIB = polyisobutylene.
U.S. Pat. No. 3,769,368 sets forth a process for preparing a grafted copolymer wherein a homopolymer is formed with a benzene ring at one of its ends, followed by chloromethylation of said benzene ring and then cationically grafting monomer onto the chloromethyl group of said homopolymer to produce only PIB-PSt copolymer.